The most successful anti-fouling paints in recent years have been self-polishing anti-fouling paints which use binders which are linear polymers containing pendant side groups (hereinafter called "leaving groups") which are liberated from the polymer by reaction with seawater, the residual polymer being sufficiently dispersible or soluble in seawater to be swept away from the paint surface, exposing a fresh lyer of the binder able to undergo a similar reaction with seawater. Such paints are described for example in British Pat. No. 1457590. The gradual thinning of the paint film controls the release of a biocide active against fouling and present either as a pigment in the paint or as a leaving group. The wellknown benefits of such self-polishing paints are that the paint film tends to at least retain its initial smoothness and may even become smoother from the action of relatively moving water and that the biocide contained in the paint tends to be delivered from the surface at a more uniform or constant rate.
The only commercially significant self-polishing paints employ binders which comprise triorganotin ester leaving groups. The triorganotin provides some of the biocidal action of the paints and the triorganotin ester readily undergoes the hydrolysis of which the self-polishing action is dependent. The biocidal activity can be augmented by other anti-fouling substances dispersed or dissolved in the paint film. There may be advantages in replacing some or all of the triorganotin leaving groups by other leaving groups, which are not necessarily biocidal, both for cost reasons and because the powerful biocidal effects of triorganotin may not be desired. There has been concern about the environmental effect of triorganotin biocides released from yachts in particular.
There have been many proposals for a leaving group which substitutes for the triorganotin in forming an easily hydrolysable ester with a polycarboxylic acid polymer, but a commercial self-polishing paint in which the triorganotin moiety has been replaced is still awaited. International Patent Publication No. WO 84/02915 suggests a wide range of organic leaving groups for use in antifouling paint binders but these generally do not hydrolyse quickly enough in the conditions of use, that is in contact with natural water, such as seawater, having a pH of from 8 to 8.4.